MyAccess Sign In

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess Profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

INCREASED INTRACRANIAL PRESSURE (INTRACRANIAL HYPERTENSION)

General Principles of Intracranial Pressure

The skull contains three components that contribute to intracranial volume: the brain, its blood supply, and the cerebrospinal fluid (CSF). The brain accounts for approximately 80% of the intracranial volume, the arterial and venous blood approximately 10%, and the CSF approximately 10%. The skull is fixed and can only accommodate small changes in intracranial volume before intracranial pressure rises. Increased intracranial pressure can arise due to increased volume of any of the three intracranial contents (brain, blood volume, or CSF).

Increased intracranial pressure due to increased blood volume—Increased blood volume can occur either due to decreased venous outflow (e.g., venous sinus thrombosis) or due to increased arterial blood flow (e.g., due to cerebral vasodilation).

Increased intracranial pressure due to increased cerebrospinal fluid volume—Increased CSF volume (hydrocephalus) can occur due to obstruction of CSF circulation or rarely due to increased CSF production (e.g., due to choroid plexus papilloma). Obstruction of CSF circulation can be caused by a blockage anywhere within the ventricular system (e.g., tumor, intraventricular hemorrhage, congenital aqueductal stenosis) or a blockage of the arachnoid granulations where CSF is absorbed into the venous circulation (e.g., due to meningitis, subarachnoid hemorrhage). Ventricular obstruction causes noncommunicating hydrocephalus: The ventricles cannot communicate with one another to allow for CSF to circulate. In noncommunicating hydrocephalus, only the ventricles proximal to the obstruction will dilate (e.g., obstruction of the third ventricle will lead to dilation of the lateral ventricles but not the fourth ventricle). Obstruction of the arachnoid granulations causes communicating hydrocephalus: The ventricles can still communicate with one another, but CSF cannot be reabsorbed. In communicating hydrocephalus, all of the ventricles will dilate.

If brain volume increases, there is the possibility of limited compensation in the other two compartments (CSF and blood) to maintain constant intracranial volume (Monro-Kellie doctrine). The compensatory mechanisms include displacing CSF into the spinal column, constriction of arterioles, and collapse of veins. However, if intracranial volume increases beyond a certain point, compensation is no longer possible, and ICP rises.